The AU1 epitope is represented by the amino acid sequence DTYRYI, derived from the major capsid protein of bovine papillomavirus-1 (BPV-1). It is a commonly used epitope tag engineered onto either the N- or C- terminus of a protein of interest so that the tagged protein can be analyzed and visualized by immunochemical methods.


Also derived from the major capsid protein of bovine papillomavirus-1 (BPV-1), the AU5 epitope is mapped to the amino acid sequence TDFYLK. AU5 is a very commonly used epitope tag that can be engineered onto the N- or C- terminus of a protein of interest so that the tagged protein can be analyzed and visualized by immunochemical methods. Due to the short sequence, this modification is not likely to affect the structure or function of the recombinant proteins.


Cre-recombinase is a 38kD DNA recombinase derived from the P1 bacteriophage and consists of 343 amino acids. It is highly specific for a 34 bp DNA sequence (loxP) found in P1 DNA. It requires no energy cofactors, such as ATP, to carry out its recombination function. The products of this recombination event depend on orientation and location of the loxP sites.


c-Myc tag (or Myc tag) originated from the c-myc proto-oncogene, cellular homolog of the avian v-myc gene in humans. It is only 10 amino acids long (EQKLISEEDL) and this small size tag does not perturb (or enhance) protein function. It can be fused to the C-terminus or the N-terminus of a protein, or even inserted within a protein. Multiple epitope tags can significantly enhance the sensitivity of detection of the fusion protein. This has been extensively used for western blotting, immunoprecipitation, and flow cytometry.


DYKDDDDK tag, commonly called Sigma's FLAG® tag, is the second fully functional epitope tag to be published in the scientific literature. Unlike other tags where a monoclonal antibody was first isolated against an existing protein, the FLAG® epitope was an idealized, artificial design to which monoclonal antibodies were raised. This has been extensively used for protein purification, western blotting, immunoprecipitation, and flow cytometry. To improve the detection of the FLAG® tag the 3x FLAG® system has been developed. This three- tandem FLAG® epitope is hydrophilic, 22-amino-acids long, and efficient for detection of low abundance proteins. If used at the N-terminus of the protein, the FLAG® tag can be removed by treatment with enterokinase, which is specific for the five N-terminal amino acids of the FLAG peptide.

E. coli RNA Polymerase

Our reagent, clone NT73, can be utilized to detect E. coli RNA polymerase and is designed to recognize Softag 1. Softag 1 is an immunoaffinity system appropriate for purifying tagged proteins from eukaryotic expression sources. The epitope (SLAELLNAGLGGS) is derived from a subunit of prokaryotic RNAP.


Green fluorescent protein (GFP) is ~29 kDa fluorescent protein used as versatile marker for visualization of protein localization, monitoring physiological processes and for detecting transgenic or transient protein expression. GFP can be used for the generation of fusion proteins without significantly interfering with native protein assembly and function, which makes this tag a very powerful tool for in vivo analyses.


The Glu-Glu tag, CEEEEYMPME, was originally isolated from the polyoma virus medium T antigen and can be incorporated into the C- or N-terminus of a protein of interest. This tag is often used as a protein modification in order to simplify the labeling and detection of proteins. The short sequence of Glu-Glu is unlikely to affect the structure or function of modified proteins. BioLegend’s epitope tag antibody, clone Glu-Glu, is capable of recognizing both EYMPME and EFMPME sequences.


GST (glutathione S-transferase) was one of the first epitope tags to be used and is ~26 kDa in size. Single-step purification of polypeptides as fusions with GST was first described as early as 1988. It can be placed on the N or C-terminus and can enhance the solubility of expressed proteins. GST tag is relatively large compared with other common peptide based epitope tags, and it may interfere with some protein functions. In these cases, it may be easily removed by protease cleavage.


The HA tag is derived from the surface glycoprotein of human influenza hemagglutinin (HA) molecule corresponding to amino acids 98-106. This segment is chosen due to its high immunogenicity and immuno-inaccessibility in the native hemagglutinin conformation. The HA epitope, YPYDVPDYA, has been widely used as a tag in recombinant protein expression vectors. This tag does not appear to interfere with the bioactivity or the biodistribution of the recombinant protein. The tag facilitates the detection, isolation, and purification of recombinant proteins.


Also known as a polyhistidine or hexa histidine-tag, this tag consists of at least six histidine (His) residues in tandem. It is extensively used for purification of recombinant proteins due to the affinity of the tag towards several types of immobilized metal ions under specific buffer conditions, including nickel, cobalt, and copper. The His-tag sequence can be placed on the N- or C-terminus of a target protein by using commercially available cloning vectors. This tag is often followed by a cleavage site for a specific protease to remove the tag after protein purification.


The ~43-kDa maltose-binding protein (MBP) is encoded by the malE gene of E. coli K12. MBP is a monomeric protein. Usually, the protein of interest is expressed as a MBP-fusion protein. Once added to the recombinant protein, MBP can increase the solubility of over- expressed fusion proteins in bacteria, especially eukaryotic proteins. The mechanism by which MBP increases solubility is not well-understood. A spacer sequence coding for ten asparagine residues between the MBP and the protein of interest increases the chances that a particular fusion will bind tightly to the amylose resin. The MBP-tag can be easily detected using immunoblotting and immunoprecipitation. The MBP can be fused at the N- or C-terminus of the protein.


mCherry is a second generation fluorescent protein derived from DsRed, a red fluorescent protein related to GFP, isolated from disc corals of the genus Discosoma. The 'm' in the name refers to its monomer configuration. The prototype for such fluorescent proteins is Green Fluorescent Protein (GFP), which is a ~27 kDa protein isolated originally from the jellyfish Aequoria victoria. mCherry is resistant to photobleaching, is quite stable, and has an extremely rapid maturation rate.

RNA Polymerase TFIIB

Our reagent, clone IIB8, can be utilized to detect RNA polymerase TFIIB by recognizing Softag3. Softag 3 is an immunoaffinity system appropriate for purifying tagged proteins from prokaryotic expression sources. The epitope (TQDPSRVG) is derived from a subunit of eukaryotic transcription factor TFIIB.


S-tag or S-15 is an epitope tag derived from first 15 N-terminal amino acids, KETAAAKFERQHMDS, of the pancreatic ribonuclease A (RNase A). When the RNase A is digested with enzyme subtilisin, it yields two components, S-peptide and S protein, which remain together and have full enzymatic activity of the parent protein (now called RNase S). The separation of components abolishes enzymatic activity, but when they are mixed together again, fully active RNase S is re-formed. This unique property of reconstituting enzymatic activity by mixing the S tag peptide and S-protein fraction enables sensitive quantitative measurement of S-tagged fusion protein by a simple assay.


The Strep-tag is a selected eight amino acid peptide (WRHPQFGG) that has intrinsic binding affinity towards streptavidin and has been extensively used for purification for membrane embedded recombinant proteins. The tag can be placed at the C- or N-terminus. Due to its small size, the tag does not interfere with folding or bioactivity, and does not induce protein aggregation.


The T7 epitope tag is composed of an 11-amino acid long peptide encoded from the leader sequence of the T7 bacteriophage gene 10. A major T7 capsid protein is encoded by gene 10, but its function is not clear. Due to the small size of the tag, it does not affect the tagged protein's biochemical properties. The tag is commonly engineered onto the N- or C- terminus of a protein of interest and is useful for the detection of proteins using immunoblotting, immunoprecipitation, and immunostaining techniques. The T7 tag has been used extensively as a general epitope tag and is commonly available in many commercial expression vectors including pET vectors.


Thioredoxin is an 11.7 kD E. coli cytoplasmic protein that act as an anti-oxidant in cells. When used as a fusion partner to produce recombinant protein, thioredoxin has been shown to increase protein solubility and yield, as well as reduce protein aggregation and precipitation.


The V5 tag is derived from the RNA polymerase α subunit of simian parainfluenza virus type 5 and corresponds to amino acids 95-108. The V5 epitope represents GKPIPNPLLGLDST and can be used to detect expression of recombinant proteins in bacteria, yeast, insects, and mammalian systems.


This tag is derived from the vesicular stomatitis virus (VSV), which is a negative-strand RNA virus. The VSV genome encodes for 5 proteins: N, P, M, G, and L. The G protein (glycoprotein) is located at the virion surface and is responsible for virus attachment and penetration. The VSV-G antibody recognizes the five C-terminal residues of the tag (YTDIEMNRLGK). Like many tags, it is commonly available as a cassette in commercially available vectors to aid cloning.